The Osprey 3 Liter HydraForm Reservoir design sandwiches an anatomically shaped molded plastic sheet between a layer of nylon fabric and the reservoir back. This forces the reservoir to conform to the back’s complex shape, even when full. The result is a more precise, stable and comfortable fit. Additionally, this reservoir has a rigid handle/spine that stabilizes the load of the water while also serving as a more convenient design to slide the reservoir into the pack.